That sound you hear is my broken record..
I actually have an anecdote which I've mentioned in threads about rough idle in 300Es a couple of times. I tried running regular for a tank to see its effect on idle in my car. My tech said MB sent out a service bulletin that said the original injectors don't operate that well with current fuel formulations (they've been redesigned), that regular burns hotter and therefor isn't as dependent on spray pattern for complete burn and that knock wasn't going to be a problem. Sure enough, I tried it and voila, smooth idle, easier starting and no appreciable loss of either power or fuel mileage. Someone on the other thread was baffled about the mileage. I was too. I don't know the physics well enough to explain it (JCE?).
I burn the mid half the time and premium the other half. Occasional Techron on long freeway trips as well. Like John, the only thing that affects my mileage is length of trips and average speed. The longer the trip at speed, the better the mileage, which means driving to Georgia should be pretty cheap.
2003 Dodge Durango SLT
2002 BMW E39 530i Sport
1988 Mercedes 300TE
2003 Chevrolet Suburban